| Summary: | The Pacific margin of South America was predominantly a subduction margin throughout the Mesozoic and Cenozoic. In the mid-Cretaceous, the continental margin arc from southernmost South America to southern Peru changed from a near sea-level, "neutral" arc to a subaerial, compressive arc. Only minor terrane accretion occurred in the central and southern Andes during this subduction episode (Darwinia and Canta terranes), but there was extensive Cretaceous-Tertiary accretion of oceanic terranes in the northern Andes (Villa de Cura, Cordillera de la Costa, Amaime, Cauca-Macuchi, Pinon, and Baudo terranes). These oceanic additions to the continent were primarily by an oblique subduction/strike-slip process. The development of an uplifted continental margin arc in the Eocene, shedding coarse sediments to the east, followed the accretion of the Cretaceous oceanic terranes in the northern Andes. The Paleozoic tectonic evolution of the Andean margin, in contrast to the Mesozoic-Cenozoic subduction-dominated evolution, shows a tectonically varied margin in space and time. In the central to southern Andes, lower Paleozoic continental margin terranes (Puna and Precordillera terranes) accreted against a margin that displays lower Paleozoic magmatic arc, as well as rift assemblages. Outboard of these terranes are continental terranes (Arequipa and Chilenia terranes) characterized by Precambrian or lower Paleozoic basement that were in place by the Carboniferous. In the late Paleozoic, subduction complexes (Chiloe and Magallanes terranes) were accreted during development of the late Carboniferous continental margin arc in the southern Andes. In the northern Andes, terranes of continental character were also emplaced (Zamora, Eastern Cordillera and Merida terranes) inboard of the younger oceanic terranes, but their final accretion was a result of the late Paleozoic collision of Gondwana and Laurentia. Late Ordovician and Devonian-Early Carboniferous orogenies affected substantial parts of the Andean margin. A magmatic arc developed along the southern Andes following these orogenies, and it continued into the Mesozoic-Cenozoic without major interruption. A Mesozoic-Cenozoic arc eventually extended the length of western South America, with the subduction process producing the present Andean Cordillera, primarily as a result of Neogene orogeny.
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